By Washington Laboratories, Ltd., Gaithersburg, Maryland
Trends in military-systems spending are driving the procurement of sophisticated systems. These systems create challenges for designers, with system testing paramount to maximizing mission success.
Military budgets are growing at rates not experienced since the Cold War. Budgeting is rooted in concern over world events and potential threats to US and international security.
This concern is pushing the development of defensive and offensive weapon systems to counter the elusive nature of the threats, where fast-strike response is critical. Sophisticated sensors, intelligence-gathering devices, highly accurate guided weapons, and integrated communications systems are all needed to achieve the aims of defense and war planners.
To accommodate mission objectives, designs must be small, lightweight, durable and reliable. This pushes packaging design issues related to denser concentration of electronics. That, in turn, creates challenges for thermal management, power handling, and electromagnetic interference (EMI) control.
In addition to fitting more into tighter spaces, the growing use of wireless technologies for control and communication creates more activity in an already-crowded RF spectrum. Add the threat of electronic warfare and the re-emergence of electromagnetic pulse (EMP, or the E-Bomb) as a potential systems-crippling weapon, and the technical challenges ratchet higher.
The severe environment of the battlefield (electromagnetic, thermal, and mechanical) is wrapped into a general classification dubbed "Environmental Effects." Let's take an overview of the tests that are mandated to assess systems against these environmental issues.
Where Does The Dough Go?
Reflecting a major shift toward defensive federal spending since September 11, 2001, military budgets are on the rise. This graph shows the rise in planned budgets for the next several years.
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Note that the Fiscal year (FY) 2004 budget calls for nearly $400 billion in allocation for national defense, representing 16% of the entire federal budget. That's approximately 13% higher than spending during the Cold War.
This equates to a "burn rate" of nearly $43 million/hour, not including the estimated $100 billion for the Iraq war.
This budget includes many items that reflect the prominence given to special forces, spy planes, and precision-guided bombs, such as those used in Afghanistan and Iraq
The table here shows the allocation of the FY2004 budget for these programs, and items requiring funding.
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Of all these items, the combined categories of Procurement and R&D, Testing, and Evaluation consume $134 billion of the budget. That's a huge sum of money in anyone's reckoning.
The largest single program in the budget is $9.1 billion for missile defense; that's an increase of $1.5 billion over last year. In FY2004 ten land-based missile interceptor systems are planned to be located in California and Alaska, with an additional ten more to be added in FY2005. These funds are slotted under R&D and include no procurement amounts, as the systems haven't yet passed development testing.
Detailed allocations of significant weapons systems are shown in the following table. These systems represent highly computerized and automated systems that require a high level of integration to operate as intended.
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What's common in these procurements is the increasing sophistication of the electronics required to execute the designed missions. Environmental issues, reliability, and EMC (electromagnetic compatibility) are concerns.
For airborne and soldier-carried systems, weight and size restrictions put design demands on packaging of equipment. Often, these restrictions raise potential design tradeoff issues. Lighter packages may lead to less robust mechanical designs. Thinner material, or the use of composites to save weight, may affect shielding performance.
An example of sophistication is the Predator Unmanned Aerial Vehicle (UAV). The Predator is a remote-controlled aircraft, capable of flying at 25,000 feet, but controlled by a pilot over a C-band line-of-sight data link, or a Ku-band satellite data link for beyond line-of-sight flight.
The UAV is equipped with a color nose-camera (generally used by the aerial vehicle operator for flight control), a daylight variable-aperture TV camera, a variable-aperture infrared camera (for low light/night), and a synthetic aperture radar (SAR) for looking through smoke, clouds, or haze.
The cameras produce full-motion video, and the SAR provides still-frame radar images. The Predator can be equipped with Hellfire anti-tank weapons, with guidance systems integrating electro-optical, infrared, laser designation, and laser illumination---all in a single sensor package.
To accomplish its intended mission, the environmental effects that impact the design and packaging of such a system must be considered. Thermal management, heat dissipation, cabling and wiring must all be considered.
Removing waste heat from dense electronics mandates the use of innovative thermal transfer systems, such as heat pipes and conduction systems. As many military systems must be environmentally sealed to prevent moisture and corrosion, the use of air-cooling is often not a ready option.
Power management, including reducing supply voltages, using hibernation techniques, and selective use of precious battery power, is paramount for mission success and serves to reduce unwanted heat.
The soldier in modern combat also carries sophisticated communications and sensor technologies, including laser-assisted targeting, video-capture, electro-optical systems, night vision, and mine avoidance.
Providing power to these electronic systems requires conventional techniques, such as portable generator/ charging systems, solar cells, and fuel cells. More unconventional sources of energy include the "power boot," which contains a system of chambers, fitted into a boot, which drive air back-and-forth through tiny turbines as a soldier walks. These turbines are connected to generators, which produce electrical power.
The requirement to provide long-lasting sources of power is pushing the state-of-the art in battery design. It's requiring the development of exotic metallurgy to store power, charge cells quickly, and maintain necessary voltage during an entire discharge cycle.
To validate the operation of equipment under anticipated environmental conditions, two critical specs have been developed, and have been applied to military systems.
The current EMC standard is MIL-STD-461E. The principal environmental specification is MIL-STD-810F.
An overview of the tests specified in these documents is provided below. Earlier versions of MIL-STD-461 (prior to revision D of the document) required tailoring of the specification. This left much to the interpretation of the test personnel. Version D brought more specific practice, limits, and procedures in order to limit variation in the results.
The severity and limits for the tests are often tailored to location on a vehicle or installation. For example, equipment located below-decks on a surface ship may have to meet a level of radiated susceptibility of 10-V/m, but equipment located above-decks, say, in the pilothouse, chart room, signal shelter, or helicopter control station, must meet a higher limit of 200-V/m (or possibly greater than 1000-V/m.
Proper circuit, package, cabling, and power-system design achieve EMC. Click here for design guidance.
MIL-STD-810F calls out specific tests to simulate the environmental conditions during operation. The list of tests is tailored according to the installation and operating location of the system.
These tests are normally called out in a procurement specification and may not all apply to any one system. It's critical to review the applicability of these test methods to assure that testing is appropriate and necessary, and covers potential conditions the equipment may encounter during its service life.
For the foreseeable future, ignoring any "sea change" in the world situation, the development of expensive, complex, and sophisticated military systems will proceed. At the same time, the challenges for system designers will rise with increasing sophistication. This will push packaging, EMC, and environmental performance requirements.
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